JPS63190929A - Magnetic bearing control device - Google Patents

Abstract

PURPOSE:To prevent the generation of vibration and to retain a floating body stably by subtracting the second signal which is obtained by passing one signal from a position sensor through a filter and a proportional circuit from the first signal which is the other signal from the position signal in its original condition, to be feedbacked to a magnetic bearing. CONSTITUTION:A signal from a position sensor 1 is divided into two signals. One signal is fed in its original condition as the first signal (a) to a + input end of a subtraction circuit 9, and the other signal has a frequency band portion which becomes more unstable force extracted by a filter 7, which is amplified by a proportional circuit 8 having a alpha-fold gain. After that, the signal is fed as the second signal (b) to - input terminal of the subtraction circuit 9. Thus, the signal (b) is subtracted from the signal (a) by the subtraction circuit 9. A signal (c) after such subtraction is input through a position feedback gain 2 to a control circuit 3. Thus the damping characteristics of a magnetic bearing is as shown by a solid line D, in which a dotted line portion of a frequency band of fC1-fC2 is changed into stabilization, so that natural frequencies in the frequency band are stabilized.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to turbo molecular pumps and compressors.

The present invention relates to a magnetic bearing control device that is applied to magnetic bearings for high-speed rotating bodies such as turbines and spindles for machine tools, as well as magnetic bearings for floating moving objects such as tenters.

[Conventional technology]

There are magnetic bearings that use electromagnets as a means of keeping rotating bodies and moving objects floating. This magnetic bearing has less loss than conventional fluid-lubricated bearings, allows for a dryer bearing, and a cleaner atmosphere, making it particularly useful in vacuum conditions.

In this magnetic bearing, as a means of setting the floating position of a rotating body or a running object, the floating position of the floating object is measured, and based on the measurement signal, the current value to be passed through the electromagnet is determined, and the magnitude of the magnetic force generated from the electromagnet is determined. There is a means to determine.

FIG. 5 is a block diagram showing the configuration of the control system of the means. In FIG. 5, the position sensor 1 detects the position of the floating object (
An example of this is an eddy current displacement meter. The position feedback gain 2 is for proportionally multiplying the magnitude of the signal obtained by the position sensor 1 to a required magnitude. The control circuit 3 includes a signal processing circuit for inputting the signal obtained by the position feedback gain 2 to the electromagnet 4 in an appropriate form. As this signal processing circuit, for example, PID (proportional-integral-derivative)
There are circuits, phase compensation circuits, and combination circuits. The electromagnet 4 has a coil wound around an iron core, and generates magnetic force for levitation in response to a current supplied from the control circuit 3.

Considering the simplest position feedback system in which the control circuit 3 is composed of only proportional elements (P elements), the transfer function of the input I of the electromagnet 4 and the magnetic force F which is the output is determined by the resistance and inductance of the coil, iron core, etc. It becomes the following first-order lag system.

F/I −KM / (1+7M・S) − (1) Here, K is the gain of the electromagnet 4, TM is the time constant of the electromagnet 4,
S is a Laplace operator. Therefore, the transfer function from the measured displacement of the position feedback system to the force F to the floating object is as follows.

F/D=Kr-Kp-KM/(1+TM-8)...(2) Here,
KF is the proportional gain of position feedback gain 2, KP
represent the proportional gain of the control circuit 3, respectively. In order to see the frequency characteristics of (force F)/(displacement D) of the position feedback system, a Laplace operator 5-j2πf is set and substituted into equation (2).

Here, f is the frequency (Hz) and is j--". (F)/(Displacement D) is a complex number and is expressed as follows.

F/D-KR(f)+j-KI (f)...(3) In equation (3), the real part of (force F)/(displacement D) means the stiffness depending on the frequency f, and the imaginary part means attenuation dependent on frequency f. The imaginary part of the first-order lag as shown in equation (2) is always negative, and it becomes a destabilizing force on the floating object that is opposite to damping.

FIG. 6 is a diagram showing the relationship between (force F)/(displacement D), that is, the value of the imaginary part of equation (3), and frequency f.

Dotted line A shown in FIG. 6 corresponds to equation (2),
The above state is shown. If the value of the frequency f-fc shown in Figure 6 is greater than the damping of the natural frequency fc of the floating object and the position feedback system, especially the damping of the floating object, the natural frequency will oscillate divergently. , and become unable to drive.

Therefore, the position feedback system (force F)/(displacement D)
In order to provide a damping effect to the control circuit 3, a proportional element (P
A differential element (D element) or a phase compensation element is provided in parallel with the D element. Here, a differential element (D element) will be taken as a representative example. When the differential element (D element) is realized as a circuit in the control circuit 3, the following first-order lag system is added.

(Differential element)-KD-8/(1+TD-8)...(4
) Here, KD is the gain of the differential element, and TD is the time constant. (Force F)/( of the position feedback system with only differential elements
The displacement D) is expressed by the following formula.

F/D = K F or KD-KM fist S/((1+T
D-8)(1+TM-8))...(5) Since the numerator of equation (5) is the first order of S and the denominator is the second order of S, the imaginary part of equation (5) is shown in Figure 6. It becomes like the dashed line B shown in FIG. That is, it has a damping effect on floating objects in a low frequency range, and a destabilizing effect in a high frequency range. In order to maintain the position of the floating object, the control circuit 3 requires the coexistence of a proportional element and a differential element. Such a control circuit 3
The (force F)/(displacement D) of the position feedback system is F
/ D = KF ・(KP+KD-8/(1+Tp-8))・KM/
(1+TM -S) ...(6), and becomes like the solid line C shown in FIG. 6, and the above-mentioned dashed line B
It has almost the same characteristics as . If the natural perturbation number fc consisting of the floating object and the position feedback system is placed in a low frequency range that has a damping effect, stability can be ensured and operation can be performed without generating vibrations.

When a magnetic bearing having such characteristics is used as the bearing 6 of the rotating body 5 shown in FIG. 7(a) and the rotating body 5 is levitated, the following phenomenon occurs. Rotating body 5
has a natural frequency on the infinite side as shown in FIGS. 7(b), (c), (d), (e), and (f). The damping caused by the material of the rotating body 5 itself acts as a destabilizing effect for natural frequencies below the rotational speed, and acts as a damping effect for natural frequencies above the rotational speed.

Therefore, it is necessary to bring the natural frequency of the magnetic bearing 6's position feedback system below the rotational speed to the frequency range where the damping effect of (force F)/(displacement D) exists. However, the natural frequency of the rotating body 5 is
e) (f) Since there are infinitely many as shown in ~, it is certain that
)/(displacement D) There is a natural frequency in the frequency region that has a destabilizing effect. Therefore, if the destabilizing effect of the position feedback system of the magnetic bearing 6 becomes greater than the damping of the natural frequency of the rotating body 5 itself, it becomes unstable.
The vibrations become larger in a divergent manner, making it impossible to rotate.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional device, in order to maintain the position of the floating object, the position of the floating object is measured by the position sensor 1, the signal is fed back, and force is generated from the electromagnet 4. This force becomes a destabilizing force that causes the floating object to vibrate. Even if processing such as PID and phase compensation is performed in the control circuit 3, it becomes a stabilizing (damping) force in the low frequency band, but it still has a large destabilizing force in the middle and high frequency bands. However, in a floating object such as a rotating body that has a natural frequency on the infinite side, the natural frequency always exists in the frequency band that causes a destabilizing force, so the magnetic bearing 6 generates divergent vibrations. become.

Therefore, the present invention provides a magnetic bearing that can change the destabilizing force generated by the magnetic bearing into a stabilizing force in a specified frequency band, prevent the generation of divergent vibrations, and stably hold a floating object. The purpose is to provide a control device.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the object, the present invention takes the following measures. In other words, the signal from the position sensor for the floating object is fed back to the magnetic bearing, and the PI
D In a magnetic bearing control device that performs control such as proportional, integral, and differential (proportional, integral, differential) and phase compensation, and actively uses a magnetic bearing, the signal from the position sensor is divided into two,
One signal is used as a first signal, the other signal is passed through a filter and a proportional circuit whose pass frequency band is a predetermined frequency to be stabilized, and a second signal is obtained. The reduced signal is fed back to the magnetic bearing.

[Effect]

By taking such measures, the following effects are achieved. In other words, only the frequency band portion that is a destabilizing force is extracted by a filter, this is amplified by a proportional circuit, and then subtracted from the original signal, so the frequency band portion that is a destabilizing force of the feedback signal is The polarity is inverted (the phase differs by 180') from the original signal. As a result, all forces generated by the magnetic bearing are converted into stabilizing forces.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a control system in an embodiment of the present invention. Note that parts having the same functions as those in FIG. 5 are given the same reference numerals.

In FIG. 1, 7 is a filter that passes a frequency band portion that is a destabilizing force, 8 is a proportional circuit for signal amplification, and 9 is a subtraction circuit.

FIG. 2 is a diagram showing the gain characteristics of the filter. Second
As shown in the figure, the filter 7 has a pass characteristic (gain 1) in a predetermined frequency band to be stabilized, that is, a band where the frequency f is fcm to fc2.

In this way, the signal from the position sensor 1 is separated into two, and one of the signals is directly sent to the subtraction circuit 9 as the first signal a.
The other signal is supplied to the (+) input terminal of The signal is supplied to the (-) input terminal of the subtraction circuit 9 as a signal. Therefore, the subtraction circuit 9 converts the first signal a
A second signal is subtracted from. The signal C after such subtraction is input to the control circuit 3 via the position feedback gain 2.

Assuming that (force F)/(displacement D) of the magnetic bearing is expressed by equation (3), in the path of the first signal a, F/D-KR(f) +j- in the entire frequency band of f. 1 (f)...(7). Also, since the second signal path passes through the filter 7 and the proportional circuit 8, in the band fcm to fc2, F/D-αΦKR(f)+jα·Kr(f)...
(8-1), and in bands other than fc1 to fc2, F/D
-0(8-2). Finally, the second signal is subtracted from the first signal a, so in the path of signal C, fcm to fc
In the band No. 2, F/D-(1-α) conflict KR(j) +j (1-α)・KI (f) ...(9-1), and in bands other than fc1 to fc2, F/D
-KR(f)+j -Kr(f) (9-2). As for the value of the above equation (9-1), if the gain α of the proportional circuit 8 is "1" or more, the polarity of the sign will be reversed.

FIGS. 3(a), 3(b), and 3(c) are diagrams showing signal waveforms in the band fc1 to fc2 in each path when the gain α of the proportional circuit 8 is set to "2".

3A shows the waveform of the first signal a, FIG. 2B shows the waveform of the second signal A, and FIG. 1C shows the waveform of the signal C after subtraction. As shown in the same figure (c), the above signal C
has reversed polarity.

In this way, the damping characteristics of the magnetic bearing are shown by the solid line in Fig. 4, and the dotted line E in the frequency band from fc to fc2.
The part has been changed to a stabilizing force. Therefore, the natural frequencies in the above frequency band are stabilized. Note that the amount of attenuation that contributes to the above stabilization is the gain α of the proportional circuit 8.
By appropriately adjusting the value of , it is possible to set an appropriate value corresponding to the destabilizing force. Therefore, the above-mentioned stabilization is performed reliably, and the occurrence of divergent vibrations is prevented.

Note that the present invention is not limited to the above embodiments.

For example, in the embodiment described above, the filter 7, the proportional circuit 8. Although the circuit including the subtracter 9 is provided between the position sensor 1 and the position feedback gain 2 as an example, it may be provided in other parts of the magnetic bearing control system. Further, in the above embodiment, the case where stabilization is attempted only for one frequency band from frequency fcm to fc2 was exemplified;
Depending on the characteristics of the floating object and the magnetic bearing, stabilization may be achieved in a plurality of frequency bands or in all bands above a predetermined frequency, for example, fc1. It goes without saying that various other modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, a signal from a position sensor is divided into parts, one signal is used as a first signal, and the other signal is passed through a filter and a proportional circuit whose passband is the frequency band to be stabilized. Since the signal obtained by subtracting the second signal from the first signal is fed back to the magnetic bearing, the destabilizing force is changed to a stabilizing force (damping force) in the specified frequency band. Therefore, it is possible to provide a magnetic bearing control device that can prevent the occurrence of divergent vibrations and stably hold a floating object floating.

[Brief explanation of the drawing]

Figures 1 to 4 are diagrams showing one embodiment of the present invention, in which Figure 1 is a block diagram showing the configuration of the control system, Figure 2 is a diagram showing the gain-frequency characteristics of the filter, and Figure 3 is a diagram showing an embodiment of the present invention. (a)(b)(
c) is a diagram showing the signal waveform of a predetermined frequency band in each path, and FIG. 4 is a diagram showing the damping characteristics of the magnetic bearing. Fifth
Figures to Figure 7(a)...Cf>~ are diagrams showing conventional examples,
Fig. 5 is a block diagram showing the configuration of the control system, Fig. 6 is a diagram showing the damping characteristics of the magnetic bearing, and Fig. 7 (a)...(f)
- is a diagram showing a rotating body and its natural frequency. DESCRIPTION OF SYMBOLS 1... Position sensor, 2... Position feedback gain, 3... Control circuit, 4... Electromagnet, 5... Rotating body, 6... Magnetic bearing, 7... Filter, 8... ...Proportional circuit, 9...Subtraction circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 2 = 1 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In a magnetic bearing control device that actively uses a magnetic bearing by feeding back a signal from a position sensor for a floating object to a magnetic bearing and controlling PID (proportional, integral, differential), phase compensation, etc. The signal from the sensor is divided into two, one signal is used as the first signal, and the other signal is passed through a filter and proportional circuit whose pass frequency band is a predetermined frequency to be stabilized, and becomes the second signal. A magnetic bearing control device, characterized in that a signal obtained by subtracting the second signal from the first signal is fed back to the magnetic bearing.